Here is the full list of all 27 Aquaria achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Kill the Coward.
Travel to all the areas of Aquaria.
Discover two peculiar-looking fish...
Find all the Ancient Turtles.
Learn all the songs in Aquaria.
Rescue all the lost souls.
Defeat Mom and Dad.
Find all the health eggs.
Enter the belly of the Whale.
Find all the recipes in the game.
Reach the Frozen Veil.
Defeat the King Jelly.
Defeat Octomun.
Dive into the water from a certain high location...
Devour a Parrot.
Beat the Arnassi race in less than a minute.
Defeat the Priests.
???
Fling a Monkey.
Reach the Veil.
Reach the Sprite Cave.
Defeat Mergog
Defeat the Rock Crab.
Defeat the Mantis Shrimp.
Ride Ekkrit for a minute.
Devour 6 creatues in a row.
Reach Open Waters.